Every year, about a quarter of all metal produced in the world, is lost due to development and the corrosion processes.The costs associated with the repair and replacement of equipment and communication of chemical plants, often several times higher than the cost of materials, which were needed for their manufacture.Corrosion is called spontaneous destruction of metals and various alloys under the influence of the environment.However, you can protect yourself from these processes.There are various methods of corrosion protection, as well as impacts.In the field of chemical production the most common types of corrosion are gas, atmospheric, and electrochemical.
Out of the situation
Choice of struggle in this case depends not only on the characteristics of the metal itself, but also on the operating conditions.Methods of corrosion protection are selected according to certain factors, however, and there is often a number of difficulties.A particular problem is associated with the choice of options for multicomponent medium with parameters that vary during the process.In the chemical industry it is not uncommon.Methods of protection against corrosion, used in practice, divided by the nature of their effects on the environment and the metal.
impact on the environment
Even in the Middle Ages were known, special substances that were introduced in relatively small quantities, for reduced corrosive environments.For this purpose, it was decided to use oils, resins and starches.Over the past period there were more and more corrosion inhibitors.At the moment, only Russia can count dozens of manufacturers.Corrosion inhibitors are widespread due to their affordable cost.They are most effective in systems where there is a constant or a little updated amount of the corrosive environment, for example in tanks, vessels, cooling systems, steam boilers and other chemical units.
Properties
corrosion inhibitors can be organic and inorganic nature.They can protect against liquid or gas media exposure.Corrosion inhibitors in the petroleum industry in most cases are associated with inhibition of anodic and cathodic electrochemical processes damage the formation of passivating and protective films.You can see the essence of this.
anode corrosion inhibitors act on the basis of anode passivation sections corroding the metal surface, which was the cause of the name of sequestering.As such oxidants traditionally used inorganic nitrates, chromates and molybdates.They are easily reduced at the cathode surface, because of which are similar to the depolarizer slowing transition anode in a solution containing ions of the corroding metal.
anodic moderators also considered some of the compounds that are not characterized by the presence of oxidizing properties: polyphosphates, phosphates, sodium benzoate, sodium silicates.Their action as inhibitors manifests itself only in the presence of oxygen, which plays the role of a passivating.These substances cause adsorption of oxygen on the metal surfaces.In addition, they cause inhibition of anodic dissolution process due to the formation of protective films, which consist of a difficultly soluble product and the interaction of the inhibitor of metal ions passing into solution.
Features
anode corrosion inhibitors made is classified as hazardous, because under certain conditions, they turn out to moderators initiators destructive process.To avoid this, it is necessary that the corrosion current density was higher than that at which is formed the absolute passivation anodic areas.The concentration of the passivating agent should not be reduced below the specified value, or may not come passivation, or it is incomplete.The last option is fraught with great danger, because it causes the reduction of the anode surface, increasing the depth and speed of the destruction of the metal in small areas.
requirements
turns out that you can provide effective protection in the case of the anode to maintain the concentration of inhibitor above the maximum value to all areas of the product that is subject to protection.These materials are quite sensitive to the pH range.In most cases, chromates and nitrates are used in heat exchangers and to protect the surface of the tubes.
Cathodic inhibitors
on protective action of these substances are less efficient compared to the anode.Their effect is based on the fact that local alkalinization of the medium results in the formation on the cathode portions insoluble products, the insulating portion of the surface of the solution.As such substances may act, for example, calcium bicarbonate, releasing a alkalized medium calcium carbonate as a precipitate difficult undergoing dissolution.Cathode corrosion inhibitor, the composition of which depends on the environment of use does not lead to increased destructive processes, even in low content.
Species
in a neutral environment as cathodic and anodic inhibitors often act inorganic substances, but in highly acidic solutions, they are not able to help.As inhibitors during production of acids used organic substances which contain specific molecules or polar groups, such as amines, thiourea, aldehydes, phenols and carbonate salts.
On the mechanism of action of the corrosion inhibitors are different adsorption character.After adsorption to the cathode or anode portions they strongly impede the discharge of hydrogen ions, ionization and reaction of the metal.To a large degree the protective effect is based on temperature, concentration, type of the acid anion, and hydrogen ion concentration.They are often added in small amounts, because the protective action of a number of organic inhibitors at high concentrations may be even dangerous.
For example, an organic compound called "Penta-522" - neftevodorastvorimy.It is able to provide a degree of protection of over 90% at a rate of 15-25 grams per ton.Corrosion inhibitor, manufactured under the trademark "Aminkor" - a product of the esterification of carboxylic acids, which are not volatile, do not have an unpleasant odor, nontoxic.The dose is determined only after the installation of the extent of corrosion active real medium.
effect on metals
This group of methods of protection involves the use of a variety of coatings.This paint, metal, rubber, and other types.They are applied in different ways: by spraying, electroplating, and other rubberizing.You can see each of them.
By rubberizing taken to mean corrosion protection through rubber coatings that are often required in the production of chlorine.Rubber compounds have high chemical resistance and provide protection for tanks, bathrooms, as well as other chemical equipment from corrosion and rust.Gumming is cold and hot vulcanization process which is carried out epoxy and PTFE compounds.
It is important to not only choose but also cause corrosion inhibitor.Manufacturers usually provide enough clear guidance on this issue.Currently, in addition to the galvanic deposition, the spread was fairly strong method of high deposition.With its help solve a wide spectrum of tasks.It is possible to apply powder material to obtain coatings having different properties.
Protection Equipment
Issues relating to the protection of chemical equipment, is quite specific, and therefore requires very careful consideration.The choice of materials for quality coatings requires an analysis of the surface composition of the medium, operating conditions, the degree of aggressiveness, temperature and more.Sometimes a "simple matter" is a critical parameter, which complicates the selection of the type of coating, for example, steaming even every few months a propane tank.That is why every aggressive environment requires the selection of such a film former and components for such coatings that are characterized by resistance to the reactants.
Special opinion
Experts say that can not be compared with each other thermal spray deposition methods and especially to assert that some of them are better than the other.Do any of them have certain advantages and disadvantages, and the resulting coatings have different properties, which indicates their potential to solve some of his tasks.The optimum composition, which must be characterized by the corrosion inhibitors, and their method of application are selected depending on the case.
the chemical grow back, this method is most often used in the process of maintenance.Even if the acidic corrosion inhibitors are used, it is necessary to properly prepare the surface of the first metal.The only way to ensure you receive a quality cover.Before coating directly painting material can be used blasting with which provide a sufficiently roughened surface.
Every year on the market there are more new developments, and there is considerable choice.However, chemists should decide what is more profitable - to conduct timely protection equipment or the complete replacement of all structures.
